Though economic growth slowed throughout much of the world during 2001, world carbon emissions from burning fossil fuels continued their relentless upward trend, surpassing 6.5 billion tons. As a result of the consistent growth of emissions, the atmospheric concentration of carbon dioxide (CO2) has increased from the preindustrial level of 280 parts per million (ppm) to today's 370 ppm, a 32-percent increase. In the last 20 years, the atmospheric concentration of CO2 has increased at the unprecedented rate of 1.5 ppm a year.

In 1950, carbon emissions stood at 1.6 billion tons. By 1977, that had more than tripled, to 4.9 billion tons. In 2000, carbon emissions approached 6.5 billion tons, a quadrupling in just 50 years. Since the atmosphere's capacity to fix carbon is fairly constant, as the volume of emissions rises, the earth fixes a decreasing percentage of emissions. The increased atmospheric concentrations of CO2 and other greenhouse gases (GHG) trap more of the earth's heat, causing temperatures to rise. These in turn are responsible for melting ice, rising sea levels, and a greater number of more destructive storms.

Three fourths of the carbon emissions from human activities are due to the combustion of fossil fuels; the rest is caused by changes in land use, principally deforestation. Global energy consumption is projected to rise 60 percent over the next 20 years. Coal use is expected to increase by 45 percent, oil consumption by 58 percent, and natural gas by 93 percent, according to the U.S. Department of Energy. Since coal consumption has actually declined by 6 percent since its peak in 1996, however, there is reason to believe its use will either continue to drop or will increase less than projected. Yet even if coal usage remains steady over the next 20 years, the current level of emissions from all fossil fuels is simply too high. The increasing use of fossil fuels will only exacerbate changes in global climate.

According to the Intergovernmental Panel on Climate Change (IPCC), atmospheric CO2 concentrations by 2100 will be in the range of 650 to 970 ppm—more than double or triple preindustrial levels. As a result, the global average surface temperature will likely rise between 1.4 and 5.8 degrees Celsius between 1990 and 2100, an unprecedented rate of increase.

Fortunately, changes can be made in each of these sectors to reduce carbon emissions using readily available technology. Shifting to wind, solar, and geothermal power for all electricity generation could greatly reduce the use of fossil fuels. Increased appliance and machinery efficiency could lower industrial and residential energy use. In the short term, shifts away from personal vehicles toward mass transit, along with increases in fuel efficiency, can reduce transportation emissions. And in the longer term, use of hydrogen-fueled cars and buses could cut emissions even further.

The United States is far and away the world's leading producer of carbon emissions, with 24 percent of the global total. China is responsible for 14 percent, and Russia accounts for 6 percent. Japan, whose economy is the second largest in the world, and India, whose population is second only to China, are each responsible for 5 percent of world emissions.

Various policy measures have been put forward to address climate change and reduce concentrations of CO2 and other greenhouse gases. The most prominent is the Kyoto Protocol, which commits industrial nations to reduce their emissions by at least 5 percent below 1990 levels by 2008-12. To enter into force, 55 countries representing 55 percent of emissions from industrial and former Eastern bloc nations must ratify the treaty. As of early June 2002, 74 countries responsible for 35.8 percent of global GHG emissions have ratified the protocol, including Japan and all nations of the European Union. But with the United States and Australia refusing to ratify, the likelihood that it will enter into force is considerably diminished.

In the United States, the Bush administration's "Clear Skies" proposal requires a decline in carbon emissions per unit of economic output (known as carbon intensity), but not overall carbon emissions. The flawed premise underlying the proposal is that economic growth cannot be achieved without significant carbon emission increases; thus "Clear Skies" will not fundamentally alter the U.S. emissions trajectory. The U.S. economy has consistently improved its carbon intensity, yet emissions have continued to increase. According to the American Council for an Energy-Efficient Economy, the carbon intensity of the U.S. economy was cut by 17 percent between 1990 and 2000, yet total emissions increased during that time by 14 percent due to a 39-percent increase in economic activity.

The Kyoto Protocol, even if implemented, is only a first step. According to the IPCC, stabilizing atmospheric levels of CO2 at 450 ppm would require fossil fuel emissions to drop below 1990 levels within a few decades, and eventually to decline to a small fraction of current levels.

Regardless of the ultimate fate of the Kyoto Protocol, other policy initiatives show promise. Decreasing or eliminating government subsidies to fossil fuels, which total $300 billion annually worldwide, can move the energy economy away from heavy reliance on carbon-intensive fossil fuels. Decreasing taxes on income while instituting or increasing carbon taxes would constructively align economic and environmental goals. Increasing funding for further research and development of clean energy technologies can also help move the world from a carbon-based and toward a hydrogen-based energy system. Finally, stabilizing human population sooner rather than later will help reduce future emissions.